Large cargo parachutes are typically constructed to have a flat disc canopy of approximately 100 feet in diameter, although some are smaller and a few are larger. A 100-foot diameter cargo parachute may typically be used for recovering an aerial delivered payload having a weight range from approximately 2,500 pounds to 5,000 pounds. Payloads of less than approximately 2,500 pounds would most often use a cargo parachute having a smaller diameter. If the payload weight is between approximately 5,000 pounds and 10,000 pounds, another 100-foot diameter parachute is typically added beside the original parachute. The resulting arrangement is known as a 2-chute cluster. Similarly, payload weights of between approximately 10,000 pounds and 15,000 pounds typically use three 100-foot diameter parachutes as a 3-chute cluster. Further, each approximately 5,000-pound payload weight increase typically requires an additional 100-foot diameter parachute.
The initial inflation phase of parachute deployment is typically quite dynamic and somewhat chaotic. Therefore, a typical 2-chute parachute cluster will have more inflation difficulties than will a single parachute, and each additional parachute added to a cluster further increases the potential for a parachute to fail. Because of these issues, a parachute cluster having more than eight 100-foot diameter parachutes is extremely unusual. Primarily, the problems begin with what are referred to as “leading” and/or “lagging” parachutes.
If one of the parachutes in a cluster is slow to initially ingest air (a “lagging” parachute), other inflating parachutes may block its air inlet area and it may not inflate at all. If one or more parachutes in a cluster fail to inflate, the rate of descent for the payload will be higher than desired. The payload may be damaged or destroyed at landing.
Conversely, if one parachute in a cluster of parachutes ingests air in advance of the others within a cluster (a “leading” parachute), it may become overloaded and rupture. If another parachute then leads, it too may overload and rupture. A chain reaction may follow until all parachutes in the cluster have catastrophically failed.
In an attempt to minimize these and other parachute inflation problems, large cargo parachutes are typically equipped with a “reefing” system to provide some control to the initial parachute inflation stage. A typical reefing system consists of a series of reefing rings attached circumferentially around the periphery of the parachute canopy, a reefing line, and a reefing line cutter. The reefing line is passed through the reefing rings, and prevents the parachute canopy from opening fully. Therefore, this conventional reefing system is somewhat analogous to a set of trouser belt loops, having a belt sequentially threaded through them, with the belt tightly cinched until the reefing line cutter severs it. Once the reefing line is severed, the parachute is no longer restrained by the reefing line and the parachute is permitted to fully inflate. Even with a reefing system, however, initial inflation of individual parachutes in a parachute cluster is somewhat random, and many parachute failures still occur.
Additionally, typical aerial delivery operations occur at relatively low altitudes. Therefore, reefing line cutters having short delays, such as about 2.0 seconds, are typically used. But, within a particular cluster of parachutes, these relatively short reefing times often do not provide a sufficient time interval for the reefing systems to provide optimal control of the individual parachute canopy air inlets before the reefing cutters sever their reefing lines. Delaying the disreefing event, for example by incorporating longer delay reefing cutters, may allow more time for the individual reefing systems to provide better initial parachute inflation control, but may also allow the payload to reach the ground surface before full inflation of the parachutes can occur. Therefore, while longer reefing times may improve the success rate of some aerial delivery systems, the altitude from which the aerial delivery operation occurs must be increased to allow more reefing time. This is generally an undesirable option, because most aerial delivery operations are conducted as part of larger military operations. Thus, factors other than parachute reefing times play a significant role in selecting the preferred aerial delivery altitude.
Therefore, it remains desirable to achieve a greater degree of control over the inflation process for solo and/or clustered parachutes, for example parachutes utilized for aerial delivery operations.